The wizards in The Washington Post's graphics department – I'm not kidding, I think they must have wands or something, though none are bearded – managed to answer these questions in a single infographic, which is copied below. You can see a larger version here.

The good news is that, if you're American (or British, Japanese, Russian, Canadian, Australian or Swedish), your country's Internet infrastructure makes it almost impossible for a Syria-style blackout. The bad news is that much of the world is vulnerable, though Syria's case is unusual. Here's the graphic: